The Sea of Azov port of Mariupol, reduced to a wasteland by seven weeks of siege and bombardment that Ukraine says has killed tens of thousands of civilians, could become the first big city to be captured by Russia since its invasion.

Russia said Wednesday more than 1,000 Ukrainian marines — among the last defenders holed up in the Azovstal industrial district — had surrendered, though Ukraine did not confirm that.

Here is why the city's capture would be significant: